In case of applying a pressure-sensitive adhesive to a base material (adherend) formed from a resin containing a plasticizer (e.g. vinyl chloride resin), cross-migration of the plasticizer from the base material to the adhesive has occasionally caused plasticization of the adhesive itself, resulting in drastic reduction of an adhesive strength. Therefore, a conventional pressure-sensitive adhesive occasionally causes peeling due to reduction of a strength at the bonding portion with a lapse of time, thus making it impossible to perform satisfactory bonding.
U.S. Pat. No. 4,943,461 discloses a pressure-sensitive adhesive comprising (a) a copolymer of monomers consisting essentially of about 60 to 85 parts by weight of an acrylate of a non-tertiary alcohol, an alkyl of which has about 4 to 14 carbon atoms, and about 15 to 40 parts by weight of a polar nitrogen-containing vinyl monomer, and (b) an acrylonitrile-butadiene rubber in an amount of 1 to 10 parts based on the weight of the copolymer. It is described that this adhesive is capable of maintaining an adhesive strength to a plasticized vinyl base material for a long term and use of the acrylonitrile-butadiene rubber in combination with the specific acrylic polymer has an effect of enhancing a shear resistance to the plasticized base material.
Japanese Unexamined Patent Publication No. 2-18486 discloses, as a pressure-sensitive adhesive capable of maintaining an adhesion property to the plasticized polyvinyl chloride for a long term, a pressure-sensitive adhesive comprising a copolymer of monomers consisting essentially of 60 to 88 parts of an acrylate of an alcohol having 4 to 14 carbon atoms, 2 to 30 parts of a nitrogen-containing vinyl monomer and 0 to 12 parts of a vinylcarboxylic acid, and a plasticizer in an amount of 2 to 35% based on the copolymer. However, the adhesive has the following problem. Namely, since the adhesive contains the plasticizer, the adhesion property of the adhesive per se can not be exhibited even if stable adhesion property can be maintained and, therefore, it can not help sacrificing the adhesive strength.